Image forming apparatus using recording sheet folded in half

1. An image forming apparatus comprising: a recording sheet supply portion configured to feed a recording sheet; a double-sided image forming portion capable of forming an image on each of a first recording surface of the recording sheet and a second recording surface opposite the first recording surface, respectively, of the recording sheet, while conveying the recording sheet supplied from the recording sheet supply portion; a divided image acquiring portion configured to acquire a pair of divided images each constituting a half of an original image; an image forming control portion configured to supply a folded recording sheet that is the recording sheet folded in half to the double-sided image forming portion, and cause the double-sided image forming portion to perform processing of forming the pair of divided images on the first recording surface and the second recording surface, respectively, of the folded recording sheet; a processor configured to execute a mode selecting portion, wherein the mode selecting portion is configured to select one of a first image forming operation mode and a second image forming operation mode, the first image forming operation mode being an operation mode in which the folded recording sheet is supplied to the double-sided image forming portion, the second image forming operation mode being an operation mode in which the recording sheet that is not folded is supplied to the double-sided image forming portion; and a first detecting portion configured to detect an overlapping state of the recording sheet based on levels of detection signals of transmitted waves resulting from ultrasonic waves at two detected portions of the recording sheet, wherein the image forming control portion includes a conveyance control portion configured to, when the first image forming operation mode is selected by the mode selecting portion, set a conveyance speed of the recording sheet to a lower speed than when the second image forming operation mode is selected by the mode selecting portion, wherein the two detected portions are portions of the recording sheet fed from the recording sheet supply portion that are located at positions close to opposite ends in a width direction orthogonal to a feeding direction of the recording sheet, wherein the processor is configured to determine that one of the detected portions is a folded-back portion of the folded recording sheet and select the first image forming operation mode when a level of a detection signal of each of the two detected portions that is outputted from the first detecting portion and a level difference between the detection signals of the two detected portions satisfy a predetermined first condition, and select the second image forming operation mode when the level of the detection signal of each of the two detected portions that is outputted from the first detecting portion and the level difference between the detection signals of the two detected portions do not satisfy the first condition, and wherein when the first image forming operation mode is selected by the mode selecting portion, the image forming control portion causes the double-sided image forming portion to perform processing of forming the pair of divided images on the folded recording sheet such that edges of the pair of divided images, each forming a dividing line on the original image, extend along a fold line of the folded recording sheet, with the fold line of the folded recording sheet being at one of the opposite ends of the folded recording sheet in the width direction, the one of the opposite ends being determined by a result of a comparison between levels of two detection signals of the two detected portions outputted from the first detecting portion.

2. The image forming apparatus according to claim 1 , wherein the first condition includes a condition that the level of the detection signal of each of the two detected portions and a predetermined threshold are in a fixed magnitude relationship and the level difference exceeds a predetermined value.

3. An image forming apparatus comprising: a recording sheet supply portion configured to feed a recording sheet; a double-sided image forming portion capable of forming an image on each of a first recording surface of the recording sheet and a second recording surface opposite the first recording surface, respectively, of the recording sheet, while conveying the recording sheet supplied from the recording sheet supply portion; a divided image acquiring portion configured to acquire a pair of divided images each constituting a half of an original image; an image forming control portion configured to supply a folded recording sheet that is the recording sheet folded in half to the double-sided image forming portion, and cause the double-sided image forming portion to perform processing of forming the pair of divided images on the first recording surface and the second recording surface, respectively, of the folded recording sheet; a document supply portion configured to feed a document; a double-sided image reading portion capable of reading an image formed on each of a first document surface of the document and a second document surface opposite the first document surface while conveying the document supplied from the document supply portion; a processor configured to execute a mode selecting portion and an image reading control portion, wherein the mode selecting portion is configured to select one of a first image forming operation mode and a second image forming operation mode, and the image reading control portion is configured to control the double-sided image reading portion; and a second detecting portion configured to detect an overlapping state of the document based on levels of detection signals of transmitted waves resulting from ultrasonic waves at two detected portions of the document fed from the document supply portion that are located at positions close to opposite ends in a width direction orthogonal to a feeding direction of the document, wherein the divided image acquiring portion serves as the double-sided image reading portion when images of the first document surface and the second document surface of a folded document that is the document folded in half are read as the pair of divided images, wherein the first image forming operation mode is an operation mode in which the folded recording sheet is supplied to the double-sided image forming portion, wherein the second image forming operation mode is an operation mode in which the recording sheet that is not folded is supplied to the double-sided image forming portion, wherein when the first image forming operation mode is selected by the mode selecting portion in a state in which a level of a detection signal of each of the two detected portions that is outputted from the second detecting portion and a level difference between the detection signals of the two detected portions satisfy a predetermined second condition, the image reading control portion stores a position of one of the opposite ends of the document in the width direction, as a position of edges of the pair of divided images, each forming a dividing line on the original image, the one of the opposite ends being determined by a result of a comparison between levels of two detection signals of the two detected portions outputted from the second detecting portion, and the image forming control portion causes the double-sided image forming portion to form, as the pair of divided images, images of the first document surface and the second document surface read by the double-sided image reading portion from the document supplied from the document supply portion, and wherein when the first image forming operation mode is selected by the mode selecting portion, the image forming control portion causes the double-sided image forming portion to perform the processing of forming the pair of divided images on the folded recording sheet such that the edges of the pair of divided images extend along a fold line of the folded recording sheet.

4. The image forming apparatus according to claim 3 , wherein the second condition includes a condition that the level of the detection signal of each of the two detected portions that is outputted from the second detecting portion and a predetermined threshold are in a fixed magnitude relationship and the level difference exceeds a predetermined value.

5. The image forming apparatus according to claim 3 , wherein the processor is further configured to execute an image processing portion configured to generate an enlarged image of the original image read by the double-sided image reading portion in a single-sided image reading mode, and divide the enlarged image in half to generate the pair of divided images.

6. An image forming method comprising: feeding a recording sheet using a recording sheet supply portion; forming an image on each of a first recording surface of the recording sheet and a second recording surface opposite the first recording surface, respectively, of the recording sheet, while conveying the recording sheet supplied from the recording sheet supply portion, in a double-sided image forming portion; acquiring a pair of divided images each constituting a half of an original image using a divided image acquiring portion; supplying a folded recording sheet that is the recording sheet folded in half to the double-sided image forming portion using an image forming control portion, and causing the double-sided image forming portion to perform processing of forming the pair of divided images on the first recording surface and the second recording surface, respectively, of the folded recording sheet; selecting one of a first image forming operation mode and a second image forming operation mode, wherein the first image forming operation mode is an operation mode in which the folded recording sheet is supplied to the double-sided image forming portion, the second image forming operation mode is an operation mode in which the recording sheet that is not folded is supplied to the double-sided image forming portion, and the image forming control portion includes a conveyance control portion configured to, when the first image forming operation mode is selected, set a conveyance speed of the recording sheet to a lower speed than when the second image forming operation mode is selected; detecting an overlapping state of the recording sheet based on levels of detection signals of transmitted waves resulting from ultrasonic waves at two detected portions of the recording sheet, wherein the two detected portions are portions of the recording sheet fed from the recording sheet supply portion that are located at positions close to opposite ends in a width direction orthogonal to a feeding direction of the recording sheet, and one of the detected portions is determined to be a folded-back portion of the folded recording sheet, and wherein the first image forming operation mode is selected when a level of a detection signal of each of the two detected portions that is outputted from the first detecting portion and a level difference between the detection signals of the two detected portions satisfy a predetermined first condition, and the second image forming operation mode is selected when the level of the detection signal of each of the two detected portions that is outputted from the first detecting portion and the level difference between the detection signals of the two detected portions do not satisfy the first condition; and when the first image forming operation mode is selected, causing, by the image forming control portion, the double-sided image forming portion to perform processing of forming the pair of divided images on the folded recording sheet such that edges of the pair of divided images, each forming a dividing line on the original image, extend along a fold line of the folded recording sheet, with the fold line of the folded recording sheet being at one of the opposite ends of the folded recording sheet in the width direction, the one of the opposite ends being determined by a result of a comparison between levels of two detection signals of the two detected portions outputted from the first detecting portion.

7. An image forming method comprising: feeding a recording sheet using a recording sheet supply portion; forming an image on each of a first recording surface of the recording sheet and a second recording surface opposite the first recording surface, respectively, of the recording sheet, while conveying the recording sheet supplied from the recording sheet supply portion, using a double-sided image forming portion; acquiring a pair of divided images each constituting a half of an original image using a divided image acquiring portion, wherein the divided image acquiring portion serves as the double-sided image reading portion when images of a first document surface and a second document surface of a folded document that is a document folded in half are read as the pair of divided images; supplying a folded recording sheet that is the recording sheet folded in half to the double-sided image forming portion using an image forming control portion, and cause the double-sided image forming portion to perform processing of forming the pair of divided images on the first recording surface and the second recording surface, respectively, of the folded recording sheet; feeding the document using a document supply portion; reading an image formed on each of the first document surface of the document and the second document surface opposite the first document surface using a double-sided image reading portion while conveying the document supplied from the document supply portion selecting one of a first image forming operation mode and a second image forming operation mode, the first image forming operation mode being an operation mode in which the folded recording sheet is supplied to the double-sided image forming portion, the second image forming operation mode being an operation mode in which the recording sheet that is not folded is supplied to the double-sided image forming portion; using a second detecting portion, detecting an overlapping state of the document based on levels of detection signals of transmitted waves resulting from ultrasonic waves at two detected portions of the document fed from the document supply portion that are located at positions close to opposite ends in a width direction orthogonal to a feeding direction of the document; when the first image forming operation mode is selected in a state in which a level of a detection signal of each of the two detected portions that is outputted from the second detecting portion and a level difference between the detection signals of the two detected portions satisfy a predetermined second condition, storing a position of one of the opposite ends of the document in the width direction, as a position of edges of the pair of divided images, each forming a dividing line on the original image, the one of the opposite ends being determined by a result of a comparison between levels of two detection signals of the two detected portions outputted from the second detecting portion, and causing, by the image forming control portion, the double-sided image forming portion to form, as the pair of divided images, images of the first document surface and the second document surface read by the double-sided image reading portion from the document supplied from the document supply portion; and when the first image forming operation mode is selected, causing, by the image forming control portion, the double-sided image forming portion to perform the processing of forming the pair of divided images on the folded recording sheet such that the edges of the pair of divided images extend along a fold line of the folded recording sheet.